The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An airplane nacelle is designed to surround a turbojet engine and produce the thrust for the turbojet engine by channeling the flows created by the engine. It must also be able to be opened in order to access the engine and its equipment.
Most turbojet engine nacelles comprise a fan cowl surrounding the fan case of the engine and a rear body (often the thrust reverser) surrounding the central part of the engine.
To provide access to the engine and its equipment, these two nacelle components generally open in two half-parts.
The opening of these cowls is made possible owing to the presence of hinges, generally mounted in the upper part of the nacelle, in the so-called twelve o'clock position, along a mast line, and are kept closed owing to a plurality of bolts generally mounted along a locking line in the lower portion, called the six o'clock portion.
It is of course important that after a maintenance operation, all of the bolts be closed.
To that end, it is important to be able to provide, effectively, safely and quickly, that all of the opening cowls of a nacelle are properly locked before starting up the nacelle.
Today, in most cases, this verification is based almost entirely on the vigilance of the operator performing the locking operation.
As a result, certain maintenance errors have caused a significant number of poor fan cowl closures, sometimes causing major in-flight events (opening and/or loss of a fan cowl).
One of the most frequent causes of in-flight opening is the partial closure or opening of the cowl bolts.
In that scenario, it is often difficult during a routine verification to see that one or more bolts are closed incorrectly, since locking a single bolt “positions” the cowl, which then appears correctly closed from a distance.
A clear indicator of the locking state of the nacelle cowls improves flight safety.
This indicator is crucial to alert maintenance operators or any other personnel to the fact that the locking of the cowls has not been done correctly.
One thereby avoids complete or partial destruction of the cowls during flight.
Furthermore, to provide an effective system for detecting the locking of the nacelle cowls, it must be impossible to initiate unlocking or to be able to partially unlock the cowl without the corresponding locking state indicator displaying an unlocked state.
There is also a need for a system for detecting the locking of the nacelle cowls meeting the aforementioned requirements.
In particular, electric locking detection systems for nacelle cowls are known making it possible to perform a visual check of the situation.
Such an electrical system nevertheless requires an electrical power source and is subject to any electrical failures.
Where mechanical detection systems are concerned, one of the difficulties is then making sure that the state indicator for the locking of the nacelle cowls displays an unlocked state once the first bolt is open, and vice versa, that that indicator cannot transition to the locked state unless absolutely all of the bolts are locked.
Furthermore, the existing mechanical detection systems are limited to checking the position of the handle of the bolt, whereas the desired mechanical function is the stressing of the bolts.
Thus, a mechanical detection system is known that provides for painting a bright color on a bolt handle mounted on the aerodynamic line of the nacelle. More specifically, the flank of the handle of the bolt is painted a bright color and the center of gravity of the bolt causes it to pivot such that it protrudes past the aerodynamic lines of the nacelle.
A visual inspection makes it possible to detect this orange color, which protrudes past the nacelle.
Also known is a mechanical detection system that provides for covering the bolts whereof the handle is mounted inside the aerodynamic lines of the nacelle with a hatch that provides the continuity of the lines of the nacelle.
This hatch cannot be closed when the bolt is not correctly locked, as interference is created between said hatch and the handle of the bolt.
To date, nacelles are known having a very low ground clearance, which necessarily requires that the locking indicators of the nacelle cowls be moved onto the side walls of the nacelle and above the latter.
The aforementioned systems cannot meet this requirement, making them irrelevant.
In this context, also known is a mechanical detection system for detecting the locking of the nacelle cowl able to meet the new constraints imposed by the current nacelles.
Such a system is protected by French patent application no. 10/58591, not yet published, in which a locking device is proposed between a first structure and a second structure of a cowl, comprising at least one locking pair including at least one lock bolt attached to the first structure and capable of engaging with at least one corresponding retaining means, attached to the second structure, the lock bolt being movably mounted against at least one elastic return means tending to return it to a position separated from the retaining means.
This locking device comprises a detection control rod, movably mounted between a first position in which it allows unlocking of the lock bolt of the retaining means, at least one part of the lock bolt then engaging with the control rod, so as to block it from potentially returning to a second position, and said second position in which the control rod engages with at least part of the locking pair so as to block the unlocking thereof.
However, this detection system has drawbacks.
On the one hand, it is extremely complex, multiplying the mechanical parts that must interact with each other to allow effective detection.
Furthermore, the position of the lock bolt of the locking pair is adjustable, so as to offset the leveling between the different structures of a cowl, which creates a quite variable position of the end of the lock bolt with respect to the control rod from one reverser to another.
It is thus difficult to ensure that in all scenarios, whether with extreme allowances or during deformation of parts, incorrect locking of the cowl will definitely be detected.
Furthermore, in this detection system, the detection control rod is subject to a visual indicator of the hatch type.
This assembly requires that this indicator be placed on the half-cowl bearing the lock bolt of the bolt while to open/close a bolt, one places oneself on the opposite half-cowl bearing the handle of the bolt.
Thus, this visual indicator is in fact only slightly or not at all visible to an operator having decided to open a bolt to perform maintenance on the nacelle.
This creates a risk of that operator damaging the handle of the bolt before realizing that the visual indicator was not open.
Thus, the operator must necessarily open the visual indicator before any opening of the bolt.
However, insofar as this indicator is offset with respect to the handle of the bolt, the operator must move on either side of the nacelle to open the bolts, which makes the detection system labor-intensive and not very practical.